The present invention relates to an improvement in photosensitive imaging systems of the type taught in U.S. Pat. Nos. 4,399,209 and 4,440,846, wherein a highly opaque backing is used in the photosensitive material.
Imaging systems employing microencapsulated radiation sensitive compositions are the subject of commonly assigned U.S. Pat. Nos. 4,399,209; 4,416,966; 4,440,846; 4,766,050 and 5,783,353. These imaging systems are characterized in that an imaging sheet including a layer of microcapsules containing a photohardenable composition in the internal phase is image-wise exposed to actinic radiation. In the most typical embodiments, the photohardenable composition is a photopolymerizable composition including a polyethylenically unsaturated compound and a photoinitiator and a color former is encapsulated with the photopolymerizable composition. Exposure to actinic radiation hardens the internal phase of the microcapsules. Following exposure, the imaging sheet is developed by subjecting it to a uniform rupturing force in the presence of a developer. An image transfer system in which the developer material is coated on a separate substrate as a separate developer or copy sheet is disclosed in commonly assigned U.S. Pat. No. 4,399,209. A self-contained imaging system in which the encapsulated color former and the developer material are present in one layer or in two interactive layers is disclosed in commonly assigned U.S. Pat. No. 4,440,846.
When imaging systems and particularly self-contained imaging systems of the type described in U.S. Pat. Nos. 4,440,846 and 5,783,353 are exposed and developed in a small format printer, it is often desirable to expose the imaging sheets while they are situated in a stack. To do this it is important that the exposure radiation is not transmitted through the top imaging sheet in the stack to the underlying sheets, otherwise the underlying sheets may be damaged. Additionally, there are certain applications in which it may be desirable to write or print on the back of an image. It is important that this printing not show through the support and detract from the quality of the image.